THE TERPENE GROUP 



313 



(1) Hemiterpenes C 5 H 8 



(2) Terpenes C 10 H 16 



(3) Sesquiterpenes C 15 H 24 



(4) Diterpenes C 20 H 32 



(5) Polyterpenes (C 5 H 8 )n 



and their derivatives. 



The structure of most of the compounds has been established and many 

 of the natural ones have been prepared by synthesis. 

 A few are open chain compounds, namely : 

 CH 3 , 



Myrcene 



CH 3 X 

 CH 2 



CH 

 CH 



\^=CH . CH 2 . CH 2 



, 



or 



Ocimene 



Citronellol 



Geraniol 



Linalool 

 Citral geraniol 



CH 2 . CH 2 



=CH . CH . CH= 



CH 



CH 



^C CH 2 . CHo . CH, . CH / 

 CH 3 X \CH 2 .CH 2 OH 



CH 3v CH 3 



C=CH.CH 2 .CH 2 .C/ 



^CH.CH 2 OH 



CH 3 / 



CH 3 < 

 CH 3 - 

 CH 3v 



CH,' 



X CH 3 



C=CH . CH 2 . CH 2 . C CH=CH 2 



\ 



C=CH . CH 2 . CH 2 . 



OH 

 CH 3 



Geraniol makes up about 90 per cent, of Indian geranium oil. Citral is 

 present in oil of lemons, orange, etc., and is obtained by oxidising geraniol. 

 Linalool is present in lavender oil and bergamot oil. Terpin (p. 315) is 

 formed by shaking it with acids. 



Most are hydro-aromatic compounds derived from cymene and are most 

 conveniently regarded as unsaturated hydrocarbons derived from hexahydro- 

 cymene or menthane, 



and possessing 

 the skeleton 



Menthane. 



From the saturated menthane six isomeric menthenes containing one 

 double bond may be derived : 



